Method for preparing a mineral melt

ABSTRACT

The invention relates to a method for preparing a mineral melt for mineral fibres production, in particular rock wool used for thermal and/or acoustical insulation or for fire protection, stock culture substrates, reinforcement, and filtering fibres. The inventive method consists in breaking and compacting at least industrial residual materials and correction materials which are used for regulating the required composition and viscosity of the mineral melt with a bonding agent in such a way that moulded pieces can be formed and, afterwards transferred to a melting unit. The aim of said invention is to improve a method for the preparation of a mineral melt for producing rock wool in a low-cost manner optimizing properties of produced mineral fibre articles. For this purpose the components of the moulded pieces, in particular the correction materials and/or other components of a mixture are substituted at least partially by granulated combustion products, in particular ashes or slags produced by combusting lignite and/or coat-dust, waste paper or wood chips.

This invention relates to a method for preparing a mineral melt for theproduction of mineral fibres, in particular rock wool used for thermaland/or acoustical insulation or for fire protection, substrates for thecultivation of plants, reinforcement fibres and fibres for filtrationpurposes, in which method at least industrial residual materials as wellas correction materials for regulating the required composition andviscosity of the melt are reduced in size and compacted together with abonding agent to form moulded pieces, and in which said moulded piecesare supplied to a melting unit.

Insulation materials made of rock wool serve for thermal, acousticand/or fire protection. Rock wool products are further used for thecultivation of plants or for reinforcing for example coating masses orother products or also as fibres for filtering purposes. In thefollowing the rock wool products given as an example are collectivelyreferred to as mineral fibre products.

From prior art methods are known for preparing mineral melts for theproduction of mineral fibres for thermal and/or acoustic insulation aswell as for fire protection. These mineral fibre products consist ofvitrously solidified inorganic mineral fibres that are produced with theaid of a melting process. In this melting process suitable raw materialsare melted and thereafter the resulting melt is defibred in a defibringunit. Defibring of said melt is effected for example in a so-calleddrawing, centrifugal or blowing process. In the production of insulatingmaterials or substrates said mineral fibres are wetted with bondingand/or impregnating agents either droplet by droplet or are coated withbonding and/or impregnating agents directly after the defibring, so thatthereafter the same may be interconnected point by point. Then the fibremass treated in this way may be collected, deformed and the resultingstructure fixed through the curing of the bonding agents.

Reinforcing fibres and filtering fibres are as rule not treated withbonding and/or impregnating agents.

In commerce glass wool is usually differentiated from rock woolaccording to the composition of the glass fibres. Rock wool is mainlyproduced from mixtures of broken extrusive rocks such as basalt ordiabase and small amounts of limestone, dolomite and magnesite asadditional materials, as well as broken extrusive rocks and lumpy blastfurnace slags and, if necessary, additional small amounts of limestone,dolomite and magnesite. These additional materials may be added to themechanical mixtures either independently or in different mixtures witheach other. The broken raw materials are replaced to an increasingextent by artificially produced bodies of a corresponding size, shapeand strength, which bodies are composed of various raw and residualmaterials as well as suitable bonding agents. These bodies arehereinafter referred to as moulded pieces.

Said moulded pieces may contain fine-grained broken natural rocks.Further added components are industrial residual materials, for examplethe coarser components necessarily produced in the manufacturing processlike blowpipe beads, solidified slag occuring during the regulardischarging operation of the melting furnaces together with partiallyfused residual rocks and parts of the furnace lining from fire-resistantconstruction materials as well as the insulating materials or substratesoccuring during the trimming of a continuously produced fibre web. Otherindustrial residual materials are cuttings, defective products or usedinsulating materials or substrates to be fused.

Residual materials conditional on the production are prepared for themanufacturing of moulded pieces, i.e. comminuted, ground open andthereafter mixed with correction materials.

With the aid of these correction materials the required composition ofthe mechanical mixtures is obtained which causes a uniform and rapidfusion within the melting unit. At the same time the temperature andviscosity are thereby influenced to an extent that a defibring processis achieved which takes place as efficiently and uniformly as possible.

Correction materials are for example slags from steel industry such asconverter or foundry ladle slags or melting chamber granulates from coalpower plants. As essential correction materials are considered alsomaterials which contain aluminium in an oxidic and/or metallic form.Suitable supports are crude bauxite or calcined bauxite as well asalumina melting elements which naturally may also function as a bondingagent. The corresponding utilization of oil industry catalysts which areno longer usable is known from DE 101 02 615 A1.

Correction materials containing both Al₂O₃ and metallic aluminium arethe slags described in WO 99/28252 A1 which are produced in therecuperation of aluminium from Al-scrap. These slags still contain amongothers small amounts of Na-sulphates and Na-fluorides.

Further correction materials are ores like for example haematite (Fe₂O₃)or magnetite (Fe₃O₄).

The granular and fibrous components, the internal residual materials andthe correction materials are mainly mixed with inorganic bonding agents,mostly under the addition of water, and are subsequently compacted toform moulded pieces.

Inorganic bonding agents are generally understood to be hydraulicallysetting cements like standardized Portland cements, but also all kindsof special cements like the already mentioned alumina melting elements.The bonding agent moieties in the moulded pieces amount to approx 9 to15% by weight.

After having reached a strength that is sufficient for heap storage,conveying and feeding, said moulded pieces which should normally reach aresistance to pressure of approx 3-5 MPa after 3 days for example arefed to the melting unit either together with the other raw materials oralone, however, always together with the lumpy burnables which arenecessary for the melting process. Within said melting unit the meltrequired for the fibre formation is prepared and thereafter fed to thedefibring unit. Said defibring unit is normally comprised of severalrollers revolving at a high rotational speed and arranged in an offsetfashion on top of each other.

The temperature and viscosity of the mineral melt have a considerableinfluence on the processibility in the respective defibring unit. Theoptimum processing range of the melt may accordingly be specificallyinfluenced by the selection of the raw materials. In addition, thechemical composition of the melt and of the mineral fibres produced fromit has an effect on the biosolubility, i.e. the dwell time in the humanorganism. The biosolubility results to a decisive extent from the oxidemoieties and the compounds of the silicon, aluminium, titanium, sodium,magnesium, potassium, calcium as well as their ratios to each other. Forthe biosolubility there are important for example also the boroxidemoieties.

A typical composition of a mineral melt for the production ofcommercially available biosoluble rock wool substantially is as follows:SiO₂ 34.8 to 43% by weight Al₂O₃ 17.5 to 23.2% by weight TiO₂ 0 to 2.9%by weight Fe₂O₃ 2 to 10% by weight CaO + MgO 23.3 to 31.4% by weightK₂O + Na₂O 1.3 to 6.9% by weight others <3% by weight

Starting from the above-mentioned prior art the invention is based onthe problem of improving this kind of a method for preparing a mineralmelt for producing rock wool in such a way that the costs of the rawmaterials are lowered on one side, while the properties of mineral fibrearticles to be produced are optimized, if possible, on the other side.

The solution of this problem provides that the components of the mouldedpieces, particularly the correction materials and/or other components ofthe mechanical mixture are at least partially substituted by granularresidues of combustion, in particular ashes or slags, preferably fromthe combustion of lignite and/or coal dust, paper sludge or wood chips.

Accordingly, the invention above all provides that for the production ofsaid moulded pieces the correction materials mixed with the industrialresidual materials are partially substituted by residues of combustion.

The compositions of the ashes and slags usually vary within certainlimits.

In the fluidized-bed combustion waste materials are burnt in a fluidizedbed at a temperature >800° C. For the combustion of low-calorific wastematerials fuels are admixed. The fluidized bed is produced by theaddition of fluidizing air through a tuyere bottom. Fuel and/or wastematerials may be fed to the fluidized bed by means of belt charging fromthe top onto the fluidized bed or also directly into the fluidized bedby means of worm conveyors. Within said fluidized bed the degassing andgasification of the fuel and the burn-off of the fixed carbon areeffected. Volatiles may be afterburnt or the heat recovered by means ofheat exchangers. The intense mixing and combustion which is conditionalupon the process, the good heat transmission within the fluidized bed aswell as the residence time of the hot flue gases allow fluidized-bedashes to be produced which exhibit a high degree of uniformity regardingthe humidity and chemical, mineralogical as well as granuolmetriccomposition.

Here, directly discharged bed ashes having a diameter d₅₀ of approx 0.3mm and extra fine-grained filter ashes having a diameter d₅₀ of approx0.01 mm must be differentiated, which are separated from the flue gasesproduced in the combustion in electric and fibrous filters. Due to thedesulphurization of said flue gases the ashes may containcorrespondingly formed compounds.

The same applies to the combustion of lignite and coal dusts as well aswood dusts for yielding energy and for manufacturing processes withfrequently or continuously produced low-calorific side products like forexample paper sludge burnt in a subsequent step of the process in orderto utilize for example the remaining energy or to reduce the volume forlater disposal.

In the combustion of fuels, particularly of saliferous coals and wastethere are almost regularly added sorbants like for example limestone fordirect desulphurization. This results in a concentration of alkalineearth sulphates in the ash. A comparable content of alkaline earthsulphate in the ashes or in the filter residues occurs when the flue gasdust collection is effected by means of downstream dry additive systems.

Due to their chemical composition such filter ashes not only cansubsititute a part of the correction materials in the production ofmoulded pieces but surprisingly can also extremely favourably influencethe development of the strength of the moulded pieces. This effect is tobe attributed on one side to latent hydraulic properties of some of thementioned ashes and/or to the catalytic effect on the bonding agentsthat are used and finally also to their grain sizes. So surprisingly, inthe moulded pieces bonded with Portland cement both the early strengthand the final strength increase. The final strength is not of anypractical importance here. As the early strength is reached very quicklyit is, however, possible to shorten the storage time of the mouldedpieces before using them. Unless the process requires said earlystrength to its maximum possible degree, the bonding agent moiety in themoulded pieces may be reduced. Both effects, namely the shorter storagetime and/or the reduced bonding agent moieties directly result in lowercosts.

In the following there is shown a preferred composition of ash withoutany absorbent: SiO₂ 12 to 46% by weight Al₂O₃ 8 to 20% by weight TiO₂0.2 to 2% by weight Fe₂O₃ 1 to 11% by weight MgO 1 to 10% by weight CaO8 to 31% by weight K₂O 1 to 3% by weight Na₂O 0.2 to 1.5% by weight SO₃2 to 15% by weight others <2% by weight

By the use of CaO as an absorbent the CaO-content in such an ash may beincreased to 70% and the SO₃-content to 20%. This will correspondinglydecrease the moieties of other components.

Further advantages of the inventive use of the ashes are theconsiderably improved miscibility and formability through the compactionof the materials forming the basis of said moulded pieces, due to thefine-grained structure. In view of the other components of the mouldedpieces the grain size distribution of the ashes and the other residualmaterials yet allow bulk densities to be reached which, being approx 1.4to approx 1.9 kg/dm³, are relatively high and result in huge finalstrengths, in co-operation with the bonding agents.

These mass concentrations in the moulded pieces naturally lead to higherefficiencies of the melting units. The high inner strengths of themoulded pieces allow the percentage of abrasion or chipping caused byheap storage, transportation and feeding to the melting units to be keptlow. Therefore, it is possible to maintain a high degree of flow throughthe entire packing in the frequently used shaft furnaces, whereby themelting process takes place uniformly and rapidly. Both effects alsohave a positive influence on the efficiency of the downstream defibringunit, in particular to a uniform rendering of the fibre forming process.

If the moulded pieces can be handled with great care until they finallyarrive in the melting unit, the requirements to the strength may bereduced which is usually done by reducing the bonding agent moieties.Here, potential savings of approx 5 to approx 15% by weight of thenormally used bonding agents are possible.

The essential advantages and features of the invention may be summarizedas follows:

The above-described combustion residues, particularly ashes and/or slagsand preferably filter ashes have chemical compositions which areparticularly suited for the correction of the compositions of mineralmelts for the production of mineral fibres. At the usual combustiontemperatures said combustion residues cause a reduction of the viscosityof the mineral melt. This allows for example the production of finermineral fibres more uniformly, which fact in turn positively influencesthe properties of use of the mineral fibres and the mineral fibreproducts made from these mineral fibres. At the same time such a melt iskind to the material of the defibring unit.

Moreover, the relatively huge Al₂O₃ moiety in some of the combustionresidues allows the substitution of other aluminium oxide supports. Thealuminium oxide itself favours the biosolubility of the mineral fibres.Ashes from the combustion of lignite and coal dust as well as papersludge and wood chips turned out as particularly suitable.

In addition to the above-mentioned effects on a method according to theinvention for preparing a mineral melt for the production of mineralfibre articles the method according to the invention offers theadvantage that the combustion residues that otherwise would have to bedumped can now be physically exploited.

The materials contained in the combustion residues partly have aglass-forming effect and otherwise a glass-transforming effect. Veryimportant is that through the controlled manufacturing processcomponents of the combustion residues which are actually undesired areintegrated in the glasses in a sparingly soluble form.

Besides the advantage of the combustion residues that is actuallystriven for in the production of mineral fibres, this form ofexploitation additionally reduces environmental load. This even appliesin a case where after the end of their useful life the mineral fibresare not recycled again but instead dumped.

Further important is that normally such combustion residues may beobtained cost-free, so that the production costs of such mineral fibreproducts are considerably lowered.

Due to their extra-fineness and chemical composition the above-describedcombustion residues, particularly filter ashes for example fromfluidized-bed combustion processes that occur in the combustion oflignite and/or coal dust, paper sludge or wood chips, have propertieswhich are favourable for the production of moulded pieces concerning thestrength formation of the moulded pieces. At the same time they have apositive effect on the fusion behaviour of these moulded pieces in thepreparing of a mineral melt and offer a possibility of purposefullycontrolling the viscosity of the mineral melt. Finally, these combustionresidues make a positive contribution to the improvement of thebiosolubility of the mineral fibre products that are made from thesemineral melts.

Further advantages and features of the invention will become apparentfrom the subclaims as well as from the following examples of a preferredembodiment of a method according to the invention.

According to a first example of the embodiment of the invention thereare compacted moulded pieces which consist of 38 to 64% by weight ofindustrial residual materials, 5 to 20% by weight of melting chambergranulates, 0 to 11% by weight of converter slag, 0 to 14% by weight offoundry ladle slag as correction materials, 10 to 25% by weight of Al₂O₃supports, for example bauxite, 9 to 12% by weight of cements as well as1 to 5% by weight of ashes from the combustion of paper sludge. In thiscomposition particularly the converter slag and foundry ladle slagmoieties as well as the cement moieties are reduced as compared to acorresponding composition of moulded pieces according to prior art.Therefore, this embodiment results in a considerable reduction of thecement moiety, leading to a considerable reduction of the productioncosts of the moulded pieces.

According to a second example it is provided that deviating from thefirst example the correction materials are contained in the compositionof the moulded pieces as follows: melting chamber granulates 5 to 18% byweight converter slag 0 to 10% by weight and foundry ladle slag 0 to 16%by weight.

Instead of the ashes from the combustion of paper or paper sludge thiscomposition provides the use of 1 to 5% by weight of ashes from thecombustion of wood. In this example, too there is provided aconsiderable reduction of the cement moiety, so that also in this casethe above-mentioned effect is obtained in the cost-saving.

Finally, a further example provides that there are again mixedindustrial residual materials at a percentage of 38 to 64% by weight,with a melting chamber granulate moiety of 0 to 15% by weight, converterslag moiety of 0 to 15% by weight and foundry ladle slag moiety of 0 to18% by weight as correction materials, and an Al₂O₃ support, for examplebauxite, at a percentage of 5 to 20% by weight together with 11 to 13%by weight of cement and a percentage of 5 to 25% of ash from ligniteand/or coal dust combustion. In this example, too a raw materialsubstitution by the ash takes place which is accompanied by a reductionof the cement moiety.

In the examples the correction materials are at least partiallysubstituted by granular combustion residues, namely ashes from thelignite/coal comubustion, sewage sludge combustion, wood combustion orpaper production. This results in a reduction of the required amount ofcement as an expensive bonding agent and in an improved viscositycontrol.

1. Method for preparing a mineral melt for the production of mineralfibres, in particular rock wool for the production of insulatingmaterials for thermal, acoustical and fire protection, of stock culturesubstrates, reinforcement fibres and fibres for filtering purposes, inwhich method at least industrial residual materials as well ascorrection materials for regulating the required composition andviscosity of the melt are reduced in size and compacted together with abonding agent to form moulded pieces and are supplied to a melting unit,characterized in that the components of the moulded pieces, particularlythe correction materials and/or other components of the mechanicalmixture are at least partially substituted by granular combustionresidues, in particular ashes or slags from the combustion preferably oflignite and/or coal dusts, paper sludge or wood chips.
 2. Methodaccording to claim 1, characterized in that said residual materialsconsist of solidified melts, separated spherical or spiky glassparticles and/or defective or recycled products, filter dusts from themanufacturing process, mechanical mixture residues and parts of afire-resistant furnace lining.
 3. Method according to claim 1,characterized in that said residual materials are reduced in size andmixed with the correction materials as well as the bonding agent. 4.Method according to claim 1, characterized in that said moulded piecesare fed to the melting unit together with extrusive rocks like forexample basalt and/or diabase and/or furnace slags.
 5. Method accordingto claim 1, characterized in that said combustion residues are producedby a fluidized-bed combustion.
 6. Method according to claim 1,characterized in that said combustion residues are fine or extrafine-grained, in particular with a grain size <0.05 mm.
 7. Methodaccording to claim 1, characterized in that said combustion residueshave the following composition: SiO₂ 12 to 46% by weight Al₂O₃ 8 to 20%by weight TiO₂ 0.2 to 2% by weight Fe₂O₃ 1 to 11% by weight MgO 1 to 10%by weight CaO 8 to 31% by weight K₂O 1 to 3% by weight Na₂O 0.2 to 1.5%by weight SO₃ 2 to 15% by weight others <2% by weight


8. Method according to claim 1, characterized in that said mouldedpieces contain inorganic bonding agents, in particular cement moietiesof 9 to 15% by weight.
 9. Method according to claim 1, characterized inthat said correction materials are substituted by combustion residues toan extent of 2 to 25% by weight, in particular to an extent of 2 to 5%by weight.
 10. Method according to claim 1, characterized in that saidcorrection materials consist of granular ores, for example haematite ormagnetite and/or residual materials from the power plant and/or metalproducing and working industries and are contained to an extent of 20 to50% by weight in said moulded pieces.
 11. Method according to claim 1,characterized in that said correction materials have a grain size of 0to 20 mm, in particular 3 to 7 mm.
 12. Method according to claim 1,characterized in that said correction materials include alkaline earthmaterials for viscosity reduction and/or Al₂O₃ for increasing thebiosolubility.
 13. Method according to claim 1, characterized in thatsaid combustion residues contain components from from a flue gasdesulphurization.